Electron ray indicating device



April 27, 1943. I 2,317,460

J. A. HULTQUIST ELECTRON RAY INDICATING DEVICE Filed July 25, 1940 min/r 5 J. A. HUL-TQ INVENTOR ATTORNEY Patented Apr. 27, 1943 ELECTRON RAY INDICATENG DEVICE J. Albert Hultquist, Scarsdale, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application July 23, 1940, Serial No. 346,918

10 Claims.

invention relates to electron ray indicator tubes and, more particularly, to a tuning indica- -tor for frequency modulation receivers.

In frequency modulation receivers it is extremely important that the receiver be tuned to the exact center of deviation of the transmitted wave in order to avoid distortion and noise. Previously known systems, of which I am aware, for

indicating correct tuning of frequency modulation receivers depend on the use of a meter or electron ray tube so connected as to give an indication proportional to the voltage developed on the grid of the limiter stage in the receiver, a very sensitive zero center voltmeter across the output of the discriminator stage, or a dual shadow electron ray tube with one of its associated amplifiers connected to one end of the discriminator output circuit and the other connected as a phase inverter. Correct tuning in the first mentioned system is indicated by a maximum grid potential or a closure of the shadow of the electron ray tube. However, this system is rather insensitive to variations in tuning since the response characteristic of the tuned circuits in the receiver is quite broad. It is, therefore, difficult to adjust the receiver for equal response to equal frequency deviations on each side of the midfrequency. Furthermore, the maximum response at this point in the receiver has no relation to the tuning of the discriminator stage and if any change in tuning takes place there the tuning indicator can no longer be relied upon.

In the last of the above mentioned systems proper tuning is indicated by'equal sized shadow areas on both sides of the tube. The'comparison of a two shadow area is attended with some diiiiculty since the broadest parts of the shadows are separated by a considerable distance. The use of a zero center voltmeter overcomes the foregoing disadvantages but it is expensive and easily damaged.

An object, therefore, of the present invention is to overcome the above mentioned difficulties.

A further object of the present invention is the provision of a simple, inexpensive system for indicating correct tuning of a frequency modulation receiver.

Another object of the present invention is to provide electron discharge apparatus giving an indication in the form of a plurality of substantially triangular shadow areas with variable length bases, said bases being closely adjacent for ready comparison.

Still a further object is the provision of a novel method for the comparison of the relative magnitudes of a pair of independent potentials.

The foregoing objects, and others which may hereafter appear, are attained by providing a novel form of electron ray indicator tube having a luminous coating on an anode in the form of a pair of intersecting plane surfaces between a'pair of separate emitting cathodes and shadow control electrodes. lhe line of intersection of the planes is in a plane perpendicular to a line between said cathodes. Electron beams from each of thecathodes impinging on the adjacent surface'of the anode cause the luminous material thereon to fiuoresce. The control electrodes cast triangular shadows on the anode, the width of the shadow at the apex of the anode being proportional to the voltage applied to the ray control electrodes. Since the widest parts of the shadows are closely adjacent they may be readily compared.

The present invention may also be embodied in a pair of conventional single shadow electron ray tubes with their areas placed as closely adjacent as possible, or a tube of the type disclosed in a prior Roberts Patent #2,175,700, granted October 10, 1939, may be utilized, interposing between the end of the tube and the eye of the observer a pair of reversing prisms so that the widest parts of the shadows appear adjacent to each other.

The present invention will b more fully understood by reference to the following detailed description, which is accompanied by a drawing in which Figure 1 is a circuit diagram illustrating the application of my invention to the discriminator circuit of a frequency modulation receiver; Figure 2 illustrates the type of indication given by heretofore known double shadow electron ray indicator tubes in a circuit as shown in Figur 1; Figure 3 is an end view of an embodiment of the present invention and illustrates the indication given when employed in a circuit as shown in Figure 1; Figure 4 is a view partly in section of an embodiment of Figure 3, while Figures 5 and 6 illustrate modifications of the invention.

In Figure 1, I'll indicates generally a discriminator transformer of the frequency modulation receiver. Frequency modulated signals of a nst'ant amplitude are applied to the primary H. To the secondary I2 of the transformer are connected the anodes of rectifier tube I l. The windings of the transformer are tuned to the desired frequency by means of adjustable condensers l3, I3. Across the cathodes of rectifier I4 is connected an output circuit comprising resistors I5, l6 shunted by radio frequency'by-pass conde' ers ll, I8. One end of the output circuit is grounded and the other end is connected to an audio frequency load circuit, as indicated by lead 20. The junction between resistors l and I6 is connected through a radio frequency choke 2| to a center tap on the secondary 12 of discriminator transformer It. The center tap is also coupled to condenser 22 to the high poten tial side of primary H.

The discriminator circuit, described briefly above, does not form a part of the present invention and the theory of its operation will not here be gone into. However, it is important to understand that when the circuit is properly tuned to a signal to be received the potential across resistor I5 is equal in magnitude and opposite in polarity to that across resistor l6. Therefore, no D. C. potential difierence exists between lead and ground. On one side of resonance 23 will become positive due to an increase in potential across resistor l5 and a decrease across resistor l6, while on the other side of resonance the reverse condition will be true. The theory of operation of the discriminator circuit is more completely discussed in a Seeley Patent #2,l21,l03, granted June 21, 1938, and reference maybe made to that patent for a further disclosure.

Through a decoupling circuit 25, 26 a grid 27 of an amplifier and phase inverter tube 28 is connected to the upper end of load circuit l5, IS. The time constant of circuit 25, should be high enough that the audio frequency signal is filtered out and does not appear on grid 21. Dual triode amplifier tube 28 may, of course, be replaced by a pair of physically separate triodes, if desired. Anodes 23 and 30 of the amplifier tube 28 are connected to the positive sides of a source of anode potential indicated as B+ through resistors 3| and 32. The other side of the anode potential source is grounded. The cathodes are connected together and to ground through resistor 39.

Indicator tube 33 has ray control electrodes 34 and 35 connected to anodes 29 and 3!! respectively. The anode 33 of indicator tube 33 and its cathodes 31, 38 are connected to the anode supply source in the conventional manner. The magnitudes of plate resistors 3|, 32 and the common cathode resistor 39 associated with tube 28 are so adjusted that with no potential on grid 2'! equal potentials, somewhat lower than the potential on anode or target 33, are impressed on ray control electrodes 34, 35 of indicator tube 33. The shadows cast on the luminous surface of anode 36 are, therefore, of equal size. When grid 27 has a positive potential applied thereto, the plate current through resistor 3| increases causing control electrode 34 to become more negative thus increasing the width of the shadow cast thereby on luminous surface of anode 3'6. The increased current flow through resistor 39 causes the grid 21 of the phase inverter tube 28 to become effectively more negative with respect to anode 33, decreasing the anode current through resistor 32. The potential on ray control electrode 35 of indicator tube 33 therefore becomes more positive, decreasing the width of its shadow on the luminous surface of anode 33. The reverse action takes place when grid 2'! has a negative potential applied thereto. If the electron indicator tube 33 is of the type disclosed in the Roberts Patent #2,1'75,700 an indication at resonance will be obtained as shown in Figure 2 of the drawing.

The lengths of arcs :c and y of the shaded portions of the pattern are equal when the receiver is properly tuned to the incoming signal. Likewise, when the receiver is tuned to a frequency remote from any signal applied to the receiver the same indication is obtained. As the tuning of the receiver is varied and resonance with a received signal is approached, the length of the arc of one of the shaded areas increases and that of the other decreases until a certain ratio, dependent upon the constants of the circuits and the strength of the signal, is attained. Then as resonance is still more closely approached the larger shaded area decreases in size and the smaller one increases until the lengths of arcs :1: and y are again equal. The receiver is then correctly tuned. Upon a continued variation of the tuning in the same direction, the change in size of the shaded areas is reversed until again the receiver is tuned to a frequency outside the range of any received signal and both shadow areas are again equal in size. It is somewhat diflicult to determine exactly the point of proper tuning since arcs a: and y are separated by a considerable distance and the visual comparison of their lengths is difficult.

However, when using a tube constructed according to my invention, an indication is obtained as shown in Figure 3. There it will be noted that instead of shadow areas being obtained in the form of a pair of sectors of a circle with their widest parts at some distance from each other, a pair oftriangular shadows are formed having variable length bases, said bases being closely adjacent. It will be readily seen that it is very easy by inspection to determine the relative sizes of the bases of the two triangles, perfect resonance being indicated by a diamond shaped shadow area.

Figure 4 shows partly in section a perspective View of a tube constructed according to my invention. The form of the bi-planar anode or target 36 is clearly shown in this figure. Ray control electrodes 34 and 35 and cathodes 31 and 38 are constructed in the same manner as described in the heretofore mentioned Roberts patent. Likewise, shielding caps 40 and 4| are provided over the ends of the cathode and ray control electrodes in order to shield the eye of the observer from the direct light of the cathodes and in order to prevent fluorescence of the glass envelope 42 of the tube. If desired, semi-cylindrical shells supporting caps 40 and 4| maybe substituted for supporting rods 43 in order to prevent fluorescence on the sides of the glass envelope 42'. Furthermore, in some cases it may be desirable to provide a low wall bisecting the ex-- ternal angle between the planes of anode 36 for this same purpose, and to prevent a spill-over of fluorescence at the apex of the anode. The wall, being thin and in a plane parallel to the line of sight of the observer causes no obstruction to vision. Grids 31' and 38' may surround cathodes 31 and 38 for limiting the space cur rent drawn from the cathodes if desired. The elements within the glass envelope 42 are supported in position by support rods 45 and mica discs 45, as is customary practice in theconstruction of thermionic discharge tubes.

A modification of the present invention is indicated in Figure 5 wherein the diamond shaped shadow effect is obtained by using a pair of con-, ventional single shadow electron ray indicator tubes of the type generally. known in the art as 6U5/6G5 tubes. These tubes 'incorporatewithgenerally by reference character 50.

in their structure an amplifier tube as well as the ray indicating and control electrodes. A pair of these tubes are substituted for the amplifier and phase inverter tube 28 and the dual shadow area indicator tube 33 in the circuit of Figure 1. The tubes are so orientated with respect to each other than the shaded areas of the luminous surface of the anodes are adjacent one another. l/Vhile in this modification the bases of the triangular areas are not as close as in the form shown in Figures 3 and 4, a reasonably accurate indication may be obtained.

A further modification is shown in Figure 6 wherein an electron ray tube of the type shown in the Roberts Patent #2,1'75,700 is used in the circuit shown in Figure 1. The tube is indicated In order to place the broadest parts of the shadow areas adjacent a pair of reversing prisms and 52 are placed between the end of the tube 50 and the eye of the observer. These prisms may be formed of glass or any of the recently discovered transparent synthetic plastics such as Lucite. The operation of prisms 5| and 52 is well understood by those skilled in optical art and it is not believed necessary to discuss their operation further than to say that because of their interposition the widest parts of the shadow areas on anode 53 of tube 50 appear to be closely adjacent so that they may be readily compared.

In each of the forms of my invention described above, an instantaneous check of the condition of the indicating system may be had by tuning the receiver away from any signal or by removing the rectifier tube M. The absence of a diamond-shaped shadow area as shown in Figure 3 indicates that the balance of the indicating circuit has become disturbed through variation of the circuit elements or aging of the tubes. Resistors 31 and 32 must be varied to again arrive at a balance or amplifier tube 28 and/or indicator 3'3 replaced.

While I have particularly shown and described several modifications of my invention, it is to be distinctly understood that my invention is not limited thereto but that improvements within the scope of the invention may be made.

I claim:

1. The method of determining the amplitude relationship of a pair of variable potentials which comprises electrically producing a pair of luminous areas, said areas appearing adjacent one another, producing substantially triangular shadows on said areas, the bas lengths of each of said triangular shadows being visually in contact with one another throughout their lengths and controlling the base lengths of each of said shadows in accordance with the amplitude of one of said potentials.

2. Means for determining the amplitude relationship between a pair of variable potentials including a target coated with a fluorescent material, means for bombarding said target with electrons to produce a luminous pattern, control electrodes for deflecting electrons from two zones of said pattern to produce substantially triangular shadow areas, said areas, having a constant height and a variable base length, the bases of each of said areas visually appearing substantially in contact with one another throughout their length and means for applying one of said potentials to each of said control electrodes.

3. In a circuit as described, a resistor adapted to have a potential varying in polarity and amplitude impressed thereacross, a thermionic discharge tube having a bi-pla'nar anode with a luminous material thereon, means for directing a stream of electrons on adjacent areas of said anode, ray control electrodes adapted to cast triangular shadows on the luminous areas of said anode, said triangular shadows having constant heights and bases variable in length in proportion to potentials applied to said ray control electrodes, said bases appearing adjacent each other whereby their equality may be visually determined, means for varying the potential on one of said control electrodes in direct proportion to the potential across said resistor and means for varying the potential on the other of said control electrodes in inverse proportion to the potential across said resistor, said potential varying means being so adjusted that for zero potential across said resistor said triangular shadows form a diamond-shaped figure.

4. In a circuit as described, a resistor adapted to have a potential varying in polarity and amplitude impressed thereacross, a thermionic discharge tube having an anode in the form of a pair of intersecting plane surfaces, said anode having a luminescent material thereon, a pair of cathodes for directing a stream of electrons on adjacent areas of said anode whereby said areas become luminous, ray control electrodes adapted to cast triangular shadows on said luminous areas, said triangular shadows having constant heights and bases variable about a mean length in proportion to potentials applied to said ray control electrodes, said bases appearing adjacent each other whereby their equality may be visually determined, means for varying the potential on one of said control electrodes in direct proportion to the potential across said resistor and means for varying the potential on the other of said control electrodes in inverse proportion to the potential across said resistor, said potential varying means being so adjusted that for zero potential across said resistor said triangular shadow bases assume their mean length.

5. In a circuit as described, a resistor adapted to have a potential varying in polarity and amplitude impressed thereacross, a thermionic discharge tube having a cathode, a dish-shaped anode surrounding said cathode and having its interior surface coated with a fluorescent material for receiving electrons from said cathode to produce a luminescence on said anode, a pair of control electrodes disposed on opposite sides of said cathod and positioned between the cathode and anode for casting substantially triangular shadow areas on the fluorescent surface of the anode, means for impressing a potential on one of said control electrodes directly proportioned to the potential on said resistor, means for impressing a potential on the other of said control electrodes inversely proportional to the potential on said resistor and means for so modifying the appearance of the pattern cast by said control electrodes that the widest portions of said pattern appear adjacent one another.

6. In a circuit as described, a resistor adapted to have a potential varying in polarity and amplitude impressed thereacross, a thermionic dis-'- charge tube having a cathode, a dish-shaped anode surrounding said cathode and having its interior surface coated with a fluorescent material for receiving electrons from said cathode to produce a luminescence on said anode, a pair of control electrodes disposed on opposite sides of said cathode and positioned between the cathode and anode for casting substantially triangular shadow areas on the fluorescent surface of the anode, means for impressing a potential on one of said control electrodes directly proportioned to the potential on said resistor, means for impressing a potential on the other of said control electrodes inversely proportional to the potential on said resistor, and a pair of reversing prisms over said dish-shaped anode for causing the outer edges of said shadow areas to appear adjacent one another. 7

'7. In a circuit as described, a resistor adapted to have a potential varying in polarity and amplitude impressed thereacross, thermionic discharge apparatus having a pair of anode surfaces with luminous material thereon, means for directing a stream of electrons on said surfaces, ray control electrodes adapted to cast triangular shadows on said luminous areas, said triangular shadows having constant heights and basesvariable in length in proportion to potentials applied to said ray control electrodes, said bases appearing adjacent each other whereby their equality may be visually determined, means for varying the potential on one of said control electrodes in direct proportion about a mean value to the potential across said resistor and means for varying the potential on the other of said control electrodes in inverse proportion about a mean value to the potential across said resistor, said potential varying means being so adjusted that for zero potential across said resistor said trangular shadows form a diamond-shaped figure.

,8. The method of determining the amplitude relationship between a pair of variable potentials comprising the steps of producing a pair of shadows, each having one constant dimension and one variable dimension, the variable dimension of said shadows appearing visually in contact with one another and controlling the magnitude of said variable dimension of each of said shadows in accordance with the amplitude of one of said potentials.

9. The method of determining the amplitude relationship between a pair of variable potentials comprising the steps of producing a pair of shadows having at least one variable dimension, the said dimension of said shadows appearing in contact with one another throughout the length of at least one of said shadows and controlling the magnitud of said dimension of each of said shadows in accordance with the amplitude of one of said potentials.

10. In a circuit, as described, a resistor adapted to have a potential varying in polarity and amplitude impressed thereacross, thermionic discharge apparatus having luminescent anode surfaces, means for directing electron streams on said surfaces, ray control electrodes adapted to deflect said streams from portions of said surfaces to cause substantially triangular shadows thereon, said triangular shadows having bases variable in length in proportion to potentials supplied to said ray control electrodes, said bases appearing in contact with each other whereby their equality may be visually determined, means for varying th potential on one of said control electrodes in direct proportion about a mean value to the potential across said resistor and means for varying the potential on the other of said control electrodes in inverse proportion about a mean value to the potential across said resistor, said potential varying means being so adjusted that for zero potential across said resistor said triangular shadows form a diamond-shaped figure.

J. ALBERT HULTQUIST. 

